The invention relates generally to phosphor blends for wavelength conversion, and specifically phosphor blends for use in fluorescent lamps. More particularly, the invention relates to phosphor blends for use in a fluorescent lamp, and a fluorescent lamp employing the same.
A fluorescent lamp typically has a transparent glass envelope enclosing a sealed discharge space containing an inert gas and mercury vapor. When subjected to a current provided by electrodes, the mercury ionizes to produce radiation having primary wavelengths of 185 nm and 254 nm. This ultraviolet radiation, in turn, excites phosphors on the inside surface of the envelope to produce visible light which is emitted through the glass.
Generally, a fluorescent lamp for illumination uses a phosphor which absorbs the radiation generated by mercury discharge, with the wavelengths 185 nm and 254 nm, and is activated so as to convert the radiation into visible light. In some conventional fluorescent lamps, a white-emitting calcium halophosphate phosphor, such as Ca10(PO4)6(F, Cl)2:Sb,Mn, has been used. However, in order to improve the color-rendering properties and emission output of white light, a three-band type fluorescent lamp is provided which employs the proper mixture (or blend) of red, green and blue-emitting phosphors, whose emission spectrum occupies a relatively narrow band. The phosphor blend converts the most part of the radiation generated by the lamp into visible light. In such a three-band type phosphor lamp, the emitting colors of the respective phosphors are considerably different from one another. Therefore, if the emitting intensity of any of the three corresponding phosphors is decreased, color deviation occurs, degrading the color-rendering properties of the lamp.
The highest efficiency is currently obtained with phosphors containing rare earths (or rare earth-activated phosphors). The phosphor's emission in the green spectral is essentially obtained due to the terbium (Tb) emission, and red due to europium (Eu) emission. However, rare earth, especially terbium is an expensive material; it increases the cost of the phosphor blend, and therefore the cost of a discharge lamp.
Therefore, it would be desirable to provide new and improved phosphor blends for white light emission.